Studies will be continued on the dispersion of sub-micron heparin particles in coatings of poly(d, 1-lactic acid) (PLA), and characterization of the coatings in terms of heparin release rate (in buffers, de-ionized water and plasma) and in vitro thromboresistance in rotating Chandler loops. In addition, the development of the methods for producing PLA sutures containing dispersed heparin will be continued. The heparin release rate from the sutures will be measured, and the degree of control of release will be established. Focus in this year will be on establishing the correlation between the properties measured in vitro and the behavior of the materials in vivo. Both sutures and coated prostheses will be tested in dogs to assess patency and long-term thromboresistance. Particular attention will be given to the thickness of the neointinima developed at steady state, to assess the promise of these coatings for use on small-diameter prothesis.